In a conventional carriage-style printer, the paper (or other recording medium) is successively advanced such that a portion of the paper is located within a print zone. While the paper is held stationary, a printhead is moved along a carriage scan direction that is substantially perpendicular to the paper advance direction, and marks are made by the printhead on the paper in the print zone as the printhead moves past.
An example of such a carriage style printer is an inkjet printer, where the printhead includes an array of nozzles arranged in an array direction that is substantially parallel to the paper advance direction. The print zone within which printing may be done corresponds to the region between the two endmost nozzles in the array. The printhead and at least a portion of the ink supply for the printhead are typically located on a carriage which moves back and forth along a carriage guide rail. For good image quality, it is important to position the nozzles within a predetermined range of acceptable distances from the paper in the print zone. If the nozzles and the corresponding printhead face are positioned too close to the media support that holds the recording medium, the printhead can undesirably strike a sheet of recording medium in the print zone, particularly if the recording medium is thicker than anticipated, or if the recording medium is cockled, dog-eared, or otherwise not held flatly against the media support. On the other hand, if the nozzles and the corresponding printhead face are positioned too far from the media support, jets that are misdirected land further out of position on the recording medium than they would if the nozzles were closer to the recording medium. The resulting misaligned spots result in objectionable image artifacts.
In many carriage-style printers, the carriage guide rail is a round rod, and the carriage includes a corresponding rounded recess or bushing which slides along the round rod. The carriage guide rail bears the weight of the carriage and is primarily responsible for the accurate travel of the carriage. A second rail, i.e., the anti-rotation rail is used to make contact with an extension of the carriage in order to fix the carriage rotational orientation about the carriage guide rail axis. The anti-rotation rail can be a second round rod, but it can typically be made more cost effectively out of sheet metal as shown in, for example, U.S. Pat. No. 5,368,403.
One method used in the prior art to adjust the spacing between the printhead nozzle face and the paper is to adjust the interface between the extension of the carriage and the anti-rotation rail, such that the carriage is allowed to rotate forward about the carriage guide rail to position the printhead nozzle face closer to the media support, or is caused to rotate backward about the carriage guide rail to position the printhead nozzle face farther from the media support. Typically such carriage rotation positions are not locked into place. In some cases this allows for the user changing the spacing between the printhead and the recording medium during a printing job or between printing jobs. However, the adjustment mechanisms to enable such spacing changes can be complex.
What is needed is a simple adjustment mechanism and method for setting a spacing between the printhead and the media support after the printer has been assembled in the factory, and locking the setting in place.